Energy efficient highway addressable remote transducer soft modem

Abstract

A method and a highway addressable remote transducer (HART) soft modem device for modulating and demodulating analog signals with HART messages are provided. A phase coherent frequency shift keying (FSK) modulator modulates and transmits analog signals with HART messages, and a phase coherent FSK demodulator receives and demodulates the analog signals with the HART messages. The FSK modulator is a digital modulator that outputs 1 or 0 for transmission. With oversampling and low pass filtering, the digital modulation results in low jitter and good signal to noise ratio. The FSK demodulator applies a fast energy detect algorithm and dynamically reduces or increases a clock speed of a central processing unit (CPU) of the HART soft modem device for reducing power consumption of the CPU. Furthermore, the HART soft modem device uses direct memory access (DMA) to further reduce the power consumption, thereby reducing the overall power consumption by around 50%.

I claim: 
     
       1. A method for performing energy detection and determining a speed of a clock of a central processing unit of a highway addressable remote transducer soft modem device, said method comprising:
 receiving digitized analog samples from a high pass filter of a phase coherent frequency shift keying demodulator of said highway addressable remote transducer soft modem device, by an energy detector of said phase coherent frequency shift keying demodulator; 
 comparing signal amplitude of said received digitized analog samples with predetermined threshold values by said energy detector; 
 detecting presence of a valid highway addressable remote transducer analog signal when said comparison results in a value greater than said predetermined threshold values, and increasing said speed of said clock of said central processing unit of said highway addressable remote transducer soft modem device to a predetermined high frequency value; 
 setting an energy detect count value to a predetermined value and decrementing said energy detect count value, by said energy detector, when said signal amplitude of said received digitized analog samples is less than said predetermined threshold values; and 
 detecting absence of said valid highway addressable remote transducer analog signal by said energy detector, when said energy detect count value is less than zero and reducing said speed of said clock of said central processing unit of said highway addressable remote transducer soft modem device for reducing power consumption of said central processing unit. 
 
     
     
       2. The method of  claim 1 , further comprising maintaining a protocol timing of said highway addressable remote transducer soft modem device by using separate clocks for said central processing unit and peripherals of said highway addressable remote transducer soft modem device. 
     
     
       3. The method of  claim 1 , wherein said predetermined threshold values comprise a predetermined upper threshold value and a predetermined lower threshold value.